Retinal vessel occlusion is a blockage in one of the tiny veins or arteries that supply the retina - the layer of light-sensitive cells lining the back surface of the eye.

Occlusion of the retinal artery is a sight-threatening emergency. If blood flow is not re-established within a few hours, death of the light-sensitive cells produces permanent loss of vision in the affected eye.

Blockage may be due to a blood clot, or more often, an embolus from a blood clot or a fragment of atherosclerotic...